The United Nations population division recently predicted that the global population of humans would reach seven billion by Halloween.

We have every reason to be concerned about that figure, Worldwatch Institute executive director Robert Engelman says.

Writing in Yale's Environment 360, Engelman notes that humanity has tacked on an additional one billion people in a mere 12 years. (In the last 60 years, we've added a breathtaking 4.5 billion people.) Meanwhile, our food supply and energy reserve has not expanded to keep pace.

In a lengthy essay, Engelman outlines several reasons why the trend spells trouble.

Here are seven of them:

The sheer size of our population requires us to care about our impact on the rest of the world's ecosystems. "We must care, ever more with each generation, how much we as individuals are out of sync with environmental sustainability," he writes.

Counter to the hype, it's not your fault directly. "Our diets, our modes of moving, and our urge to keep interior temperatures close to 70 degrees Fahrenheit no matter what is happening outside — none of these make us awful people. It's just that collectively, these behaviors are moving basic planetary systems into danger zones."

Density may boost sustainability, but that won't solve the real problem. "Space, of course, has never been the issue. The impacts of our needs, greeds, and wants are. We should bemoan — and aggressively address — the gross inequity that characterizes individual consumption around the world."

Get real: you can't green yourself out of existence. "We should also acknowledge that over the decades-long span of most human lifetimes, most of us are likely to consume a fair amount, regardless of where and how we live; no human being, no matter how poor, can escape interacting with the environment, which is one reason population matters so much."

China's growth is just one piece of the puzzle. "More immediately worrisome from an environmental perspective, of course, is that the United States and the industrialized world as a whole still have growing populations, despite recent slowdowns in the growth rate, while already living high up on the per-capita consumption ladder."

Water scarcity is the canary in the coal mine. "Fresh water is now shared so thinly that the United Nations Environment Program projects that in just 14 years two thirds of the world's population will be living in countries facing water scarcity or stress."

The bottom line: we're out-of-balance with our surroundings. "We appropriate anywhere from 24 percent to nearly 40 percent of the photosynthetic output of the planet for our food and other purposes, and more than half of its accessible renewable freshwater runoff."

Sobering words, indeed. But anyone can criticize. Who will be bold enough to suggest -- and enact -- solutions?

Engelman rightly notes that fear won't help anyone, and we can't stop inevitable global population growth in the short term. What we can do, however, is "put in place conditions that will support an early end to growth."

His two suggestions:

Lower birth rates simply by letting women decide to become pregnant for themselves.

The problem as I see it is economic; that is, where's the leverage? This is a long-term economic strategy that comes at the expense of short-term economic gains -- a hard sell when nations are competing against each other to their own apparent long-term detriment.

In the age of globalization, can we work toward a common goal? First we may need a global organization that has the teeth to enforce it.